As the easy-to-access and easy-to-produce hydrocarbon resources have been depleted over the last century, more and more difficult wells remain. Also, as global hydrocarbon demand is continuously growing, meeting this demand requires development of more advanced recovery procedures, often referred to in industry as complex recovery completions and production techniques. These techniques include, for example, Steam Assisted Gravity Drainage (“SAGD”), Thermal Assisted Gravity Drainage (“TAGD”), Toe to Heel Air Injection (“THAI”), Vaporized Hydrocarbon Solvent (“VAPEX”) production and Fire Flooding. Such techniques address the mobility problem of the heavy oil wells by thermally and/or chemically altering the viscosity of the bitumen to allow for easy extraction.
While each of the complex completion techniques offer a solution to the issue of heavy oil extraction, they all rely on a common challenge facing wellbore construction—the precise placement of adjacent local cased wellbores. With SAGD and TAGD, injector wells must be precisely placed within a few meters of the production well, with the injector well being placed a few meters on top of the producer. Traditionally, this has been accomplished by placing both the injector and producer wellhead within a few meters at surface. The second well drilled in the well pair subsequently “follows” the in-situ cased wellbore using some magnetic ranging method.
However, due to issues such as location footprint constraints, infield drilling requirements and producer well replacement, it is often desired that a new producer or injector well be re-drilled from a separate location. This location is often selected so that the end of the lateral insitu well is approached by a new drilling well from the opposite direction. However, due to the increased wellhead to wellhead distance and the uncertainty associated with traditional surveying based on gravity and earth's magnetic fields, the precise distance between the two wells cannot be achieved. Also, in the case of the THAI method, it is required that the toe of the horizontal cased wellbore be intersected with a directional well, a requirement which cannot be met using traditional surveying techniques alone.
To address the precision wellbore placement requirement of these “opposite approach azimuth” complex completion methods, industry standard magnetic ranging tools have been deployed, such as the Magnetic Guidance Tool (“MGT”) and Rotating Magnetic Ranging Service (“RMRS”). However, these techniques are not optimal, as the accuracy of the system at the range required for the particular application is limited. This limitation translates into operational inefficiency in practice, as sidetracks are often necessary to deliver the intersection or precise separation that is required. These operational inefficiencies can also translate into inefficiency in the completion and production of the well, as the well separation and/or intersection point are less than optimal.
In some complex wellbore construction projects, the primary objective is not hydrocarbon production, but rather hydrocarbon transportation. In hydrocarbon transportation projects, two wellbores drilled from opposite directions are often intersected to produce a common wellbore. This ‘utube” communication between wellbores allows the deep subterranean borehole to be completed with a common casing string and used as a pipeline for hydrocarbon transportation. While similar projects have been completed in the past with conventional magnetic ranging techniques, the same inefficiencies associated with these techniques as described above has led to cost overruns and general operational efficiency.
Accordingly, there is a need in the art for improved downhole ranging techniques to overcome these and other shortcomings in conventional approaches.